


A Gift

by lucadumpster



Series: Stay By My Side [3]
Category: Dr. STONE (Anime), Dr. STONE (Manga)
Genre: A little sprinkle of crack in the beginning, Anal Sex, Bottom Asagiri Gen, Chrome is pining for ukyo, Established Relationship, Fluff, Fluff and Smut, M/M, Mirror Sex, Multiple Orgasms, Porn With Plot, Porn with Feelings, Slight talk about past trauma, Smut, Teasing, Top Ishigami Senkuu, gen gets fucked silly
Language: English
Status: Completed
Published: 2021-03-13
Updated: 2021-03-13
Packaged: 2021-03-20 17:00:21
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,639
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/30008052
Author URL: https://archiveofourown.org/users/lucadumpster/pseuds/lucadumpster
Summary: Senku makes Gen a gift to improve their sex life and it’s the best decision he’s made yet.
Relationships: Asagiri Gen & Ishigami Senkuu, Asagiri Gen/Ishigami Senkuu
Series: Stay By My Side [3]
Series URL: https://archiveofourown.org/series/2202252
Comments: 5
Kudos: 86





	A Gift

**Author's Note:**

> I need to go to horny jail.

“We’re friends, right, Senku?” Chrome asked the scientist as he held an Erlenmeyer flask in one hand and a glass instrument to stir the off-clear liquid inside in the other.

The question had seemingly come out of nowhere and Senku looked up, an eyebrow raised in curiosity. 

“Don’t tell me you’ve gone brain dead,” the scientist said, his tone exasperated. They were supposed to be testing a piece of sedimentary rock neither scientist had come across before, not getting sentimental. 

“Okay, yeah. Stupid question,” Chrome laughed, but his face became incredulous again. “Since we’re friends, you would be able to talk to me about anything, right?” 

What was with him today? Senku put down a pair of large tongs he was using to pick up a beaker and removed his goggles. 

“Within reason…,” Senku replied. “Just spit it out. You know I hate dancing around a subject.” 

Chrome sighed through his nose. “Is there something going on between you and Gen?” 

It was a good thing the scientist had set down the glass container because he would’ve dropped and smashed it against the laboratory floor. He couldn’t help the flush that crept up his neck and the tremor through his fingers. 

“Excuse me…?” 

“Well, you two just seem to be spending a lot more time together and even live together now! I really don’t mean to intrude, but-!”

“‘But’ what?” Senku was trying his hardest to stay calm, but with the way his heart was hammering in his chest, it was proving to be difficult. 

“Um… You see… Kohaku saw. You two at the waterfall. And then told me. About you two. At the waterfall,” Chrome blurted out awkwardly, unable to look his fellow scientist in the eye. 

‘Okay, Ishigami,’ Senku thought in his head, ‘Stay calm and rational. You have no idea how much she witnessed.’

“What was it that she saw, exactly?” 

Chrome’s face started to get red, as well. He put down his equipment and gestured with his hands something unmistakable, even in the Stone Age: a circle with one hand and a finger going right through. 

“Oh, god,” was all the scientist could utter, tilting his head down. He rubbed his temples and sighed, closing his eyes. “I guess it was only a matter of time before someone found out. I didn’t exactly expect it to be this soon, though.” 

It was almost comical how wide Chrome’s eyes got at hearing Senku’s half-confession. 

“So, you did do it!” Chrome’s shocked face turned into an ecstatic smile, slapping his friend gingerly on the back. “Congrats, man! It’s not every day that your science buddy loses his V card!”

Senku pursed his lips and looked away. 

“Wait. You’re telling me that wasn’t your first time?”

“Please, stop talking.” 

Both of them fell silent, not making any move to continue working or talk. It was an extreme understatement to say the atmosphere was permeated with embarrassment. Not that Senku was embarrassed by what Gen and him shared, but more so that they had been caught literally with their pants around their ankles. 

“I was wondering… how that works between two guys,” Chrome muttered, putting his equipment away in various shelves around the room. 

Senku looked up and saw his friend’s ears gleaming red. Now, that was interesting enough for the scientist to ask his own question. 

“Is there someone you’ve taken an interest in, Chrome? Perhaps… Ukyo?”

Chrome squeaked, fumbling with a beaker that had slipped from his clammy hands. It crashed to the floor, but thankfully didn’t break. 

“I mean, it’s not that I’m not interested in him,” Chrome admitted quietly. “But, I didn’t really think it was possible. Now that I know it can happen, I’m curious.” 

Senku smirked and proceeded to brief his friend on the ins and outs of sex between two men; what to do and what to refrain from. 

“I feel like I should be repulsed, but I’m not,” Chrome said directly after the scientist’s explanation. 

Senku picked at his ear absently with his pinky and shrugged. “Yeah. Same. It’s actually… extremely enjoyable.”

After a moment of silence, the scientist’s face went almost manic with a new plan brewing in his mind. Chrome knew that look all too well. 

“Since I’ve helped you,” Senku said, “I think it’s only fair if you help me with a little project.” 

🧪 • 🧪 • 🧪 • 🧪 

It was nearing dusk, the last glimmering rays of sunlight vanishing over the trees that surrounded the village. It was gorgeous all the time in this stone world, but nighttime was spectacular. Senku always impatiently anticipated the dim twilight after the sun set and the infinite swaths of stars you could only see after the entire world had been reclaimed by nature. 

The scientist stood alone in the observatory, gazing longingly at the celestial bodies making their appearance in the silky navy blue sky. A small smile twitched up his lips and felt a comforting blanket of emotion settle over him. The sky was the precise color of Gen’s eyes and the stars reminded him of the night the mentalist had given him the telescope on his birthday; tiny glowing dots that could possibly remember a time when Senku rebuked love. How illogical. 

“Good evening, my dear,” Gen greeted from across the room. Senku hadn’t heard him enter their home. “It’s not like you to request dinner alone with me. What’re you scheming, hmm?” 

Senku turned around, that lazy smile still on his lips, sweeping the two long strands of hair that usually hung in his face back. Leave it to his mentalist to read right through him. 

“I have a surprise for you. But before that, let’s eat. I’m starving,” Senku said, turning on a couple lamps overhead and swiveling the revolving roof closed. 

Setting down a couple bowls of ramen on a tabletop, Gen pouted, poking his bottom lip out and whining, “You can’t just tell me you have a surprise for me and then not tell me.” 

“Oh, hush, mentalist,” Senku chuckled and passed a semi-cold bottle of cola to the mentalist. “This surprise has to wait until afterwards.” 

Gen took the bottle and popped the cap, gulping down the dark liquid, some of the drink spilling out the corner of his mouth and down his chin. Senku couldn’t take his eyes off the man before him, thinking how oddly erotic the sight was. Instead of licking up the cola dripping down Gen’s face like he desperately wanted to, Senku settled for swiping it away with his thumb. 

The mentalist cleared his throat and blushed, obviously embarrassed by his mishap. 

“Cola always brings out my messiest habits.” 

“I don’t think cola is the only thing that brings out your messy habits,” Senku said. Gen’s blush deepened and it was safe to say that both men were thinking about the previous day’s activities at the waterfall. 

They sat down across from each other on a couple pillows on the wood floor, eating ramen as their knees touched. Even mild contact sent a thrill through Senku. 

After a comfortable silence filled with slurping noodles and the scrape of spoons against clay bowls, Senku broke the quietness. 

“Chrome and Kohaku know about us.” 

Gen didn’t act as dramatically as Senku had expected. Instead, he set down his empty bowl and pressed his lips together. 

“I don’t mind, honestly,” Gen murmured. “Like I’ve said before, I don’t feel embarrassed over the things I find interesting. And I don’t feel embarrassed over the things I love.” He looked up and flashed that genuine smile that was reserved for Senku only. 

“I really got lucky with you being my first love,” Senku said, picking up Gen’s hand and landing a soft kiss on the back of it. “And my last.” 

It was a comment that didn’t seem a millimeter logical, but at the same time, it was ten billion percent logical. How could Senku ever care for someone else the way he did his mentalist? It was one of those things that just made sense, like a law of science. There was no need for an explanation. It just was. 

“Close your eyes, Gen. It’s time for your surprise,” the scientist said, standing up. “And no peeking.” 

The mentalist giggled and covered his eyes with both hands. “Oooh~. How exhilarating, Senku-chan.” 

Senku stepped across the room and uncovered the project Chrome and him had been working on over the course of the afternoon. It wasn’t perfect, but it would be enough to serve its purpose. 

“Okay. Open your eyes.” 

Gen moved his hands from his eyes to cover his mouth at the sight, letting out a gasp. 

It was a mirror about the size of a modern-day refrigerator. 

“H-how…? This is amazing, Senku-chan!” The mentalist crawled forward, marveling at his reflection. He traced a finger lightly over the crack on his face and ran a hand through the white half of his hair. “I look like hell.” 

“Now, that’s simply not true,” Senku said, coming up behind Gen and placed a hand on his hip, pulling the mentalist to sit in his lap. “I remembered you telling me that you can’t have sex unless you’re looking at my face. So, I thought a mirror might help with that.” 

They both stared at themselves in the mirror and said at the same time, “We look really good together.” 

Gen turned around to look at Senku, his smile gone. Instead he rested a hand against the scientist’s cheek and said with an almost somber expression, “No one has ever taken my wants or needs seriously like you do.” 

Senku obviously knew something was wrong, but what exactly was unclear. It was odd to see Gen visibly upset even if they had been dating for three months and had been a part of the Kingdom of Science together for longer. Gen wasn’t one to show his emotions so openly. It was something the two of them had in common. 

The scientist’s worry must have been written all over his face because Gen tried to muster up a smile and murmured, “I’m okay.” 

“Don’t lie to me, Gen,” Senku said seriously. 

The mentalist dropped his gaze and his hand into his lap. After a moment, Gen replied, “Something… bad happened to me while in the Empire of Might. There’s a reason why I’m so terrified of going back there other than being afraid to die. I want to forget, but it’s not that easy.” 

He didn’t need to explain any further. Senku had enough of an idea to understand what happened to Gen. And it made him feel nauseous; it made him feel the most ill he had ever felt in his entire life. 

“I understand. You don’t need to say anything else about it. I want you to know that I would never, ever do anything to hurt you. I want you to know that if you feel even the slightest bit uncomfortable, to tell me and I will stop. I promise that I’ll keep you safe. I-.”

“Senku-chan,” Gen whispered, “you’re crying.” 

“No, I'm not. I don’t cry-.” 

But, in fact, he was. A tear rolled its way down his cheek and plopped onto Gen’s forehead. He swiped the backs of his hands across his eyes, quickly apologizing. 

Gen wrapped his arms tightly around Senku, burying his face in the crook between his shoulder and neck. “Thank you for caring so much about me. You’re more selfless than you realize.” 

The scientist clutched him close and breathed in that familiar scent that always put him at ease. There was no one else in the entire world that could make him feel this way. He had never cried for another person’s sake other than his father, and that wasn’t until he learned of his old man’s own selfless acts of courage to save humanity. Even though they weren’t blood related, he and Byakuya shared many parallels in personality. 

“You bring out the best in me.” 

The mentalist looked up, tears brimming in his own eyes. He brought his lips to Senku’s and kissed him soft and slow, holding the scientist’s chin between two fingers. 

“I trust you completely,” he whispered against Senku’s lips. 

Gen turned back around to gaze at their reflection again in the mirror and a sly grin appeared on his face, immediately making Senku’s insides flip-flop. The mentalist rubbed a sensual hand from the scientist’s hip down to his thigh and squeezed thrice. 

“So,” Gen purred, “why don’t you demonstrate the purpose of this mirror, Senku-chan? I’m quite curious.”

Senku ran his own hand over the mentalist’s shoulder, down his chest and stomach, and softly grasped the crotch of his leggings. Gen sighed and tossed his head back a bit. 

“Who knew you could get aroused from such heavy topics. Are you a masochist?” Senku chuckled and rubbed his boyfriend’s growing erection through his pants. 

“In moderation,” Gen sighed, bucking his hips in time with Senku’s strokes. “And only when I love and trust my partner.” 

The mentalist’s purple robe slid down his right shoulder, exposing his pale skin, begging to be touched. Senku lowered his head and dragged his hot tongue against Gen’s bare skin, ending it with a gentle bite, his canines digging into flesh. He tasted sweet and salty and floral as usual. Senku couldn’t get enough of that elegant flavor. 

The scientist pulled the string tying Gen’s clothing together and pushed aside all the fabric and balled it up, throwing it to the floor so that the mentalist sat wearing nothing but those leggings and that high collared top. 

“Why do you insist on wearing so many layers? It’s ten billion percent a pain in the ass,” Senku murmured and he bit Gen’s shoulder again, harder this time, leaving teeth marks in the pale skin. 

Gen’s breath hitched and thrusted his hips forward at the sudden bite. “It’s to — mm! — It’s to stay modest,” he said breathlessly, trying to keep his thoughts collected. “I’ve never been fond of revealing clothes on myself.”

“Why? You have a nice body. I’m sure you would look good with a little skin showing,” Senku chuckled and grasped the mentalist’s cock harder through his leggings, making him moan louder. 

“I could say the same thing — ahh, fuck — to you, darling.”

“Touché.” 

Senku rubbed light fingers over the cloth of Gen’s top, feeling the slight raise of his nipples. The mentalist gasped and whined, almost wrenching free of Senku’s grasp. An even wider grin spread across the scientist’s lips. How could he have neglected this spot when it earned him such a satisfying reaction? 

“Are you sensitive there? Do you like your nipples played with, my mentalist?” Senku began to slowly pop the buttons open on Gen’s shirt. 

“Stop teasing me, Senku-chan!” Gen exclaimed. 

“I apologize, but your reactions are otherworldly,” the scientist said, completing the task of unbuttoning the shirt and yanking Gen’s leggings off. The hickeys he had left the day prior were a deep purple now and Senku smiled in triumph. He had done that. 

Gen locked eyes with Senku in the mirror, his face serious. “Are you going to fuck me or are you satisfied only staring?” 

The scientist reached up, grabbing the bowl of coconut oil off the table, heart thrilled. He hiked up his tunic and pulled down his underwear, rubbing his pulsing erection with the substance, holding a groan back. 

“Will you be okay with no preparation? I don’t want to hurt you,” Senku asked as his mentalist positioned himself over his cock. 

“I should be fine since we did it just yesterday. I’ll let you know if it's too much.” He slid down and gave a cry of pleasure, his whole body wracked in a shiver. 

“Geez, Gen,” Senku sighed, his cock twitching slightly inside. “You’re practically squeezing the life outta me.” 

The mentalist had both feet planted on either side of Senku’s thighs, a hand braced against his hip. He started to rock up and down, going more slowly than usual since they hadn’t prepped him. Even so, his stroke was mind boggling, having the scientist grit his teeth and make a huge effort not to flip him over and go apeshit. 

“Is this okay? I don’t have much experience being in control like this,” Gen said, a self conscious slight in his voice. 

“Look at me,” Senku said, tugging at Gen’s shoulder as he rode him, “and tell me what you think.” 

The scientist already knew what he looked like, as he could see himself in the mirror. He never knew his face could look so lustful. His crimson eyes were heavy and half-lidded, sweat beading across his brow and upper lip, cheeks as bright as red phosphorus. He quite literally felt adrenaline shock his every nerve, vein, and capillary at the same time. 

So this was what the love of his life saw every time they made love together. 

Gen must’ve been affected by the sight as well because he bounced up and down faster, slapping his ass hard against Senku’s pelvic bone, gripping the scientist’s thighs with white-knuckled fingers and digging nails. He had his tongue out, drool slipping off the end like a faucet you hadn’t turned off all the way. 

Senku turned his attention to the mentalist’s behind. His eyes widened and jaw fell slack. While the sight of his erection sliding easily in and out, skin slick and shiny from coconut oil and secretions was arousing, it was something else that caught him off guard. Something he should’ve noticed before, but never did. 

“Is that a tattoo? Above your ass?” 

The tattoo was of a single black nightshade flower, accented with small vine and leaf detailing on either side. It was a little trashy looking, but cute nonetheless. Senku ran a thumb over it, pressing a bit into the center of the flower. 

“Oh, god. That thing? I ended up failing a bet my freshman year of college and had to get a tramp stamp,” Gen said, panting between his words. 

“Did it hurt?” 

Biting his lip, Gen answered, “Maybe just a little. But, I can handle a lot.” As soon as the words passed his lips, he slammed himself all the way down onto Senku’s cock and cried out in euphoria, cumming through the fingers he grasped around his own dick. 

Senku sat in shock. It was the first time Gen had cum without facing him. He had to admit it was a sensuous sight to behold, watching him take control like that. 

“You think you can go again?” Senku asked. 

Gen nodded, eyes hazy and hair messy in tangled knots from grabbing it in ecstasy. 

“Okay. Get on your hands and knees, my mentalist, and face the mirror. I want to hit it from behind.” 

Gen did as he was told, pulling his left buttock to the side, his hole on display. “Please, don’t be too rough. I’m sensitive now.” 

‘Dear Alan Soble,’ Senku thought, naming a prominent philosopher in sex, ‘give me the strength to not lose my mind and accidentally hurt Gen. Thank you.’

The scientist rubbed his cock against the mentalist’s opening, not wanting to forget this moment. He looked so gorgeous with his ass up and back curved down. Both of them were positively quivering in anticipation. Though, Gen was starting to whimper in impatience, backing himself into Senku’s member, practically begging to be fucked again. 

“You’re always so impatient,” the scientist murmured, chuckling at Gen’s soft moans. He easily slipped inside and the mentalist grasped a needy hand against the cold mirror. He grunted as he sped up, the slap of Gen’s ass against him was music to his ears. If he believed in angels, it might sound like a choir of them clapping gently for their performance of gasps and love sounds. 

Gen pressed his face against the mirror, his hot breath making it fog up. He lifted a feeble finger and traced “I ❤️ you” in the condensation. 

Senku grabbed his hips with both hands and moved Gen back and forth, landing two quick slaps across his ass, the skin going pink as blood rushed to the surface. 

“Yes! Yes! Mmn, Senku, yes,” Gen wailed. 

“You’re such a good boy, Gen. Ten billion points to you, my love,” Senku praised him and he felt himself growing closer and more desperate. He pulled out and unloaded himself up the trench Gen’s muscles made on either side of his spine, crying out his name over and over as he rode it out. 

The mentalist’s hoarse voice mewled and splattered on the mirror, his small body collapsing to the floor. Senku’s heart clenched and he cradled the mentalist’s face in his hands in a panic. 

“Hey. Hey, did I hurt you? Did I go too hard? Are you okay? Oh, shit. I broke you. Fuuuuuuck…,” the scientist rasped, jostling Gen. 

The mentalist opened his bleary eyes and smiled dopily. “I’m okay, I promise. It just felt amazing. My body doesn’t know what to do.” 

“Let’s get you into bed. You worked really hard tonight.” 

🧪 • 🧪 • 🧪 • 🧪 

They laid curled up together on the pallet of blankets, staring up at the night sky full of stars. Senku had opened the roof again since it was still warm enough to do so. He turned to face Gen, carding his fingers through his hair. 

“You really changed my life,” Senku whispered. 

“You say the damndest things sometimes, Senku-chan. Just when I think I’ve figured you out, you come out of left field with something that leaves me speechless,” Gen laughed. He leaned towards his scientist and pecked his lips.

“You changed my life, too.” 

They stayed like that for a while, staring at the shining stars reflected in each other’s eyes, making a million wishes, all with the same outcome. 

‘Love me forever.’

**Author's Note:**

> I hope this is just as enjoyable as the other installments!!   
> I will be taking a short hiatus from this series. But, don’t be bummed. I have a complex, multi-chapter fic in the making that my friend is helping me write. (Hint: it’s a medieval dcst AU 👀) 
> 
> My [Twitter](https://mobile.twitter.com/)


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